The present invention relates generally to positioning devices. More particularly, the present invention relates to a positioning device for controlling the position of a wafer table and an exposure apparatus, including the positioning device, for manufacturing semiconductor wafers.
In an exposure apparatus, a wafer table holds a semiconductor wafer to be exposed. To compensate for the variations in the dimensions of the wafer (e.g., wafer thickness), the exposure apparatus controls and adjusts the position of the wafer table before the wafer is exposed. Conventionally, piezoelectric actuators are used to control the position of the wafer table.
A piezoelectric actuator, however, typically has a limited stroke. One way to solve this problem is to use a cantilever type mechanism in conjunction with a piezoelectric actuator. Thus, for a piezoelectric actuator of a given length, a cantilever type mechanism amplifies the stroke provided by the piezoelectric actuator.
A cantilever type mechanism, however, amplifies the stroke of a piezoelectric actuator at the expense of decreased stiffness. Thus, a cantilever type mechanism used in conjunction with a piezoelectric actuator responds slower to a given servo bandwidth than a piezoelectric actuator alone. Thus, as the stiffness decreases, more time is needed to control the position of a wafer table. This increase in time needed to control the position of a wafer table may lead to a decrease in the production rate of wafers.
In light of the foregoing, there is a need for a structure that amplifies the stroke of a piezoelectric actuator without unduly deceasing its stiffness.
The advantages and purposes of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The advantages and purposes of the invention will be realized and attained by the elements and combinations particularly pointed out in the appended claims.
To attain the advantages and in accordance with the purposes of the invention, as embodied and broadly described herein, the invention is directed to an exposure apparatus for exposing a pattern onto a semiconductor wafer. The exposure apparatus comprises an illumination system, a lens assembly, and a positioning device. The illumination system has an illumination source emitting a beam and an illumination optical assembly guiding the beam onto the pattern. The lens assembly projects the beam passed through the pattern onto the wafer held by a wafer table. The positioning device comprises a housing, a piezoelectric actuator, and a structure for moving the wafer table in a second direction. The piezoelectric actuator has a first and second end. The first end is fixedly mounted to the housing and the second end is movable in a first direction in response to a change in voltage applied to the piezoelectric actuator. The structure comprises a first joint, a second joint, a diagonal member, and a flexure. The first joint is movable in the first direction in response to the second end of the piezoelectric actuator moving in the first direction. The second joint is movable in the second direction to move the table in the second direction. The diagonal member is connected to the first and second joints at an angle with respect to the first direction. The flexure connects the diagonal member to the first joint and is bendable in response to the first joint moving in the first direction to change the angle with respect to the first direction and thereby move the second joint in the second direction.
In another aspect, the present invention concerns a device for positioning a wafer table. The device comprises a housing, a piezoelectric actuator, and a structure for moving the wafer table in a second direction. The piezoelectric actuator has a first and second end. The first end is fixedly mounted to the housing and the second end is movable in a first direction in response to a change in voltage applied to the piezoelectric actuator. The structure comprises a first joint, a second joint, a diagonal member, and a flexure. The first joint is movable in the first direction in response to the second end of the piezoelectric actuator moving in the first direction. The second joint is movable in the second direction to move the wafer table in the second direction. The diagonal member is connected to the first and second joints at an angle with respect to the first direction. The flexure connects the diagonal member to the first joint and is bendable in response to the first joint moving in the first direction to change the angle with respect to the first direction and thereby move the second joint in the second direction.
A still further aspect of the present invention is a structure for moving a wafer table comprising a first joint, a second joint, a diagonal member, and a flexure. The first joint is movable in a first direction. The second joint is movable in a second direction to move the wafer table in the second direction. The diagonal member is connected to the first and second joints at an angle with respect to the first direction. The flexure connects the diagonal member to the first joint and is bendable in response to the first joint moving in the first direction to change the angle with respect to the first direction and thereby move the second joint in the second direction.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.
Additional advantages will be set forth in the description which follows, and in part will be understood from the description, or may be learned by practice of the invention. The objects and advantages may be obtained by means of the combinations set forth in the attached claims.